Examples of basic necessary functions as a substrate for a light emitting device include high reflectivity, high heat dissipation, and long-term reliability. A representative example of a substrate having these functions is a ceramic substrate, and the ceramic substrate is manufactured by forming an electrode pattern on a plate-shaped ceramic substrate.
However, according to a trend of high power of the light emitting device, as a result of pursuing improvement of brightness by aligning multiple light emitting elements on a substrate, the size of the ceramic substrate has been increased over the years. Specifically, when a general LED light emitting device which is used at 30 W of supplying power is realized by aligning blue LED elements which are classified as medium-sized and have a dimension of approximately 500 μm×800 μm or greater or less, approximately 100 LED elements are necessary. An example of the ceramic substrate, in which approximately 100 LED elements are aligned, includes a substrate having a plane size of 20 mm×20 mm or greater and a thickness of approximately 1 mm.
When realizing an LED light emitting device which is used at 100 W or higher of supplied power, reverting to a technical invention based on an increased size of the substrate, a large ceramic substrate which can have 400 or more LED elements loaded thereon, and has a plane size of at least 40 mm×40 mm, is necessary. However, it is difficult to realize such a large ceramic substrate on a commercial base, because of three problems, which are decreased strength of a substrate, decreased manufacturing accuracy, and increased manufacturing costs, as follows.
First, since a ceramic is a basic baked material, a problem is generated in which strength is decreased when increasing the size. When increasing the thickness of the substrate to overcome this problem, both the thermal resistance and the weight increases at the same time, and material costs of the substrate also increase. In addition, when increasing the size of the ceramic substrate, not only an external dimension, but also a dimension of an electrode pattern formed on a substrate becomes easy to be deviated. As a result, this easily leads to deterioration of a manufacturing yield and an increase in manufacturing costs.
Here, in order to overcome the above-described problems of increasing the size of the ceramic substrate, for example, as described in PTL 1 to PTL 4, a substrate in which a ceramic layer, which serves as a reflecting layer, is formed on a metal base is developed. In this manner, the substrate in which the ceramic layer is formed on the metal base has high reflectivity, high heat dissipation, long-term reliability, sufficient strength, and manufacturing accuracy.